Self-modulated oscillator



Feb 3 1948, I A. v. WURMSER SELF-MODULATED OSCILLA'I'OR Filed Jan. 26, 1944 2 Sheets-Sheet 1 LOAD IV 5 N TOR A. 1/ WURMSER A 7' TOR/V5 V Feb. 3, i948. A. v. WURMSER 2,435,262

SELF-MODULATED OS 0 ILLATOR Filed Jan. 26, 1944 2 sheets-sheet 2 FIG. 3 I

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A 7'7'ORNEY Patented Feb. 3, 1948 NITED STAES a ar SELF-MODULATED osonim'roa Application January 26, 1944, Serial No. 519,747

This invention relates to an oscillator-moderator and particularly to an electric discharge oscillator of this type and therefore to an electric discharge oscillator which is self-modulating. That is, the organization of the invention comprehends in a single electric discharge device and its immediately associated circuits, means for generating the higher frequency wave, that is, the carrier Wave, and the relatively low frequency wave, that is, the modulating wave, together with means for intermodulating the same so as to effectuate the intermodulation products, namely, the side-band frequency waves. As a corollary, to indicate the comprehensibility and versatility of the invention, the organization is capable of being used as a source for either of the component frequencies per se.

The primary object of the invention is to achieve the above functions with the simplest possible circuit organization consistently with the adequate performance of such functions; with respect, for example, to the production of adequate power at each of the frequencies for which the organization is apt to be used, with respect to adequate constancy of frequencies in the device, and the like.

A specific object, the corollary of the above object, is to achieve the complex result implied by, to as large an extent as possible, utilizing circuit elements necessarily present in an organization to achieve generation of the wave of one of the component frequencies only, so that, to as great an extent as ossible, the complexity of result is not the function of a corresponding complexity of circuit organization.

Certain difficulties have attended organizations of this generic class in the prior art, these largely having to do, for example, with undesirable and unstable interactions of the two component frequencies, leading, for instance, to overmodulation or interruption of the carrier wave at the modulating frequency when a true modulation is desired.

Another specific object of the invention is to achieve the above functions without inducing any other function and, therefore, so that the output waves (either the intermodulation products or waves of the component frequencies themselves) have no impurities which are not inherently characteristic of the function. i

In what follows, it will be assumed, partly by way of illustration but also having in mind an organization in which the invention is Well adapted to be used and which has been experimentally used, that the two component frequencies have 7 Claims. (01. 250-36) particular values, within the audible frequency range, namely, 1,000 and 20 cycles. It should be understood, however, that the inventive principle is not at all limited to use at these frequencies or even to frequencies within the audible range.

The organization assumed is sometimes described as a 1,000-20-cycle oscillator or as an oscillator which gives a 1,000-20-cycle output. Such an oscillator constitutes a 1,000-20-cycle ringing source in a Well-known signaling system. This means that the output waveis an audible frequency wave having primarily a LOGO-cycle frequency but Which is interrupted or modulated (strictly a modulation, that is, a sine wave modulation, in the present instance) at 20 cycles. Such a source elaborated, as in the present instance, to make possible the capability also of deriving a 1,000-cycle and/or a 20-cycle wave per se has additional practical applications which are not of present concern.

The above objects are achieved in the above practical example by an organization comprising primarily a 1,000-cycle electric discharge feedback oscillator of the conventional conductancecapacitance type, although the particular type is relatively immaterial, which by the injection of a' small -cycle synchronizing frequency produces a 1,000-20-cycle output Wave which is, ac cordingly, locked in and controlled by the injection frequency. Instead of the above modulating and injection frequencies any other two frequencies may be used provided there is a commensurable relation between them. The exemplary 20- cycle frequency determining elements comprise a small resistance and a very small condenser instead of the alternative large condenser and inductance that would be conventionally used if the circuit generated a 20-cycle wave as an LC prime source or even instead of the large resistance and condenser of an alternative RC prime source. The organization is not a prime source as to this frequency, that is, a source as distinctive as the LOGO-cycle prime source, because the resistance and capacitance elements are adapted from existing elements of the 1,000-cycle wave oscillator, being in fact the grid resistance and capacitance elements normally used although difierently evaluated in accordance with the specific function. While such a, resistance-capacitance circuit is not fundamentally as stable a frequency-determinin circuit as an inductance capacitance combination, the use of the injection frequency, which itself is stable, obviates any difficulty of this kind. The necessity for the use iof the injection frequency source, considered as added to the necessary elements of the prototype organization, has no implications as to an increase in the size of plant or of the complexity of the circuit, since the 60-cycle (for example, having in mind the most commonly available frequency) source may be used to excite the cathode of the tube. The result in fact is a comparatively very slmple;-inexpensi ve, organization, very-well adapted .toproduce the desiredrside-band'frequency or frequencies. Further, by an analogous demodulation action a 20-cycle Wave, as such,

may be easily derived from the circuit. This last feature is important because, consistently-with the simplest and least expensive organizations-as above, the circuit would not iordinarilybeca'pw:

aspects of the tube, as in any other conventional modulatin device.

A more complete. understanding. of the invention; will be facilitated by the followingv detailed description of; thezoscillator as xemplified in tWo specific forms, ;especially lwith -reference to the drawing, in which 1 and .2 ,are.circuit..exemplifications of thc'fivlospecies, or atleast..-alter-native forms, of the invention; ;.-and

Figs. 3,-.4, -5..and*6-;are scale representations of ,osci llograms made from -.a Fig. .1 circuit and intendedhere to be of assistance to the description in-teaching the'function andoperation-ot the invention.

-With-reference to the circuit of.Fig. .1,,tube l in. cooperation with; tuned, frequency-determining circuit-2,. together withattendant circuit elements. each performing. a conventional. function, comprises ;a well-known -.type of negative grid, feedback, :spaoedischarge oscillator, 'acommonly described as a Hartley typeosoil-lator. Therein the necessary .phase reversing .feedback. .or coupling rbetween :t-he output and :input circuits. of the elect-ric discharge .tube is achieved :by the .tuned circuit since the-cathode -3 of the tube is connected 3& --a point ,1 in .the inductance consti- "tutingxa part ,of said circuit at apoint interme- .,diate :the connections from said inductance to the .oontrol elect-rode =4 and the "anode .5, this .cathode connectionrpassingv through cathode :lead -resistor;R,1,- the function of .which willbe indicated later. :Thaelectricdischarge tube that has been used .inthis i circuit, :and is intended to -be represented in ;this 'F'ig. ;-1,-is-.anRCA tube rdesignateddiSJ'Z. {Ihis -is a standard ,pentode .tube but has been used in the Fig. .1-circuit, .as is here indicated, 3.5.3111'1'1016, ethe suppressor and shield grids; being directly; connected .to the anode :so as ,to effectively constitute a portion thereof, thelconnection, of coursepbeing made externally ;of the ztube. ;It should be emphasized at this golaceithat t-he choice of tube is .not very critical randthatthe iubecould beemployed as a pentode -tube, quite analogously as in Fig. 2 to be described. ,Similarl-y, the :Fig. 2 circuit could-employ the-triode connection illustrated by Fig. 1; :Of ,course, a filamentary cathode, instead of the indirectly -heated cathode as shown, would be a o riate- 'TllB accessory or attendant electrical elements .of :the oscillator not -so ,far :described are ignite conventional. The oscillator is presumed to gen .erate the carrier irequency wave, that is, the :kQOD-cycle wave, in {the particular instance in mind. The anodeis supplied by potential source a6. thecircuit to pathodebeing completed through ground and the above resistanc R1. The connection of circuit 2 to the anode is through a capacitor Cp which, as a blocking condenser, serves to prevent the impression of potential 5 from source 6 on the frequency-determining circuit which, among other things, would result in a near short-circuit 'of said source through a part of the inductance of saidxfrequency-determining circuit. The. capacitor C and resistor R oo- 10 operate in the usual way, in relation to the associated circuit and tube elements to insure the correct control electrode bias for efiicient operation. in the-present instance, as will be more 7 apparent latensinceathe tube functions not only 5. as-.-the--amplif1er element of a feedback oscillautorgbut. also..as.-the modulating or combining .device, with respectto the two frequencies concerned, the control-electrode bias would determineear potential on a non-linear portion of the tube characteristic. The output of the circuit, considered either. as. a LOGO-cycle oscillator or, anticipating-a. later description, as an..oscillatormodulator, may be taken olT by circuit 1 connected tothe frequency-determining circuit as shown. The. impedances. into which. the .output circuit looks .at this point, makes. thisconnection appropriate for either of. these purposes, although since. the potentialsv at thisv point. partakeof those at both the control electrode and anode, the connectioncould, although less-effectively, be made at either one .of these elements alternatively.

The-elements C..and..R, whilefunctioning as above, have another function whichis an important feature of theinvention. 'These ele mentsplay aprimary role asthe frequency-determining circuit for the modulatingfrequency, 20 cycles in the example inmind. It is obvious that an .RC circuit, .as where exemplified, can performsuch function becauseofits time con stant .analogouslyes the more customary LC circuit which is .here illustrated .as determining the .LOOO-cyclefrequency. ThisRC circuit could be otherwise, placed and, if especially. placed,

it quite possibly ,could.determine.a modulating frequency by self-sustained oscillator action. However, consistently with its double role, as above, which is very greatly in-the interest of simplicity and economy .of plant, it would .not ordinarily serve .such .a .function. Accordingly, aninjection frequency, and action are required. This is achieved by the injectioncircuit 8 whereby aninjection frequency, 60 cycles in the example inmind, tendstocoercethe circuit as a whole to which it is connected to oscillate at its own frequency or, :in the alternative and as in the circuit of the invention, at a commensurablefrequency invitediby a particular tuning or time constant of an impressed circuit. In the .present instance such impressed circuit is the RC circuit which .has a time constant close to .20 cycles and .is made .to promote an oscillation of exactly 20 cycles since this is the closest .commensurable frequency with relation to the injectionfrequency. It is obvious that the injection frequency potential, which is applied across the cathode lead resistance R1, is impressed, although indirectly, on the RC circuit.

The operation of the organization as a whole should now be quite plain. The organization as a 'whole tends to oscillate at the respective component frequencies, that is, 1,000 cycles and :20 cycles, and the tube, by the non-linear relationship between control electrode potential and anode current, achieves intermodulation .of these two frequencies. The action, in the present instance, is quite conventional in triode tubes or in tubes illustrating conventional triode functions, and is sometimes known as the Van der Bijl type of modulation. The action may be thought of as changing the control electrode potential by the modulating waves so as to correspondingly modify the amplification characteristics of the tube, since the characteristic relationship between control electrode potential and anode current at a given point on the characteristic curve expresses the amplification at the corresponding point. The final result is that a modulating frequency envelope is impressed on the carrier frequency wave occurring in the anode-cathode circuit. It is apparent that with the ultimate result achieved in the particular Way illustrated by Fig. 1 there is a comparative simplicity and economy of plant. Because of the injection action this achievement is attended by no sacrifice of frequency stability because of the use of an RC, instead of an LC, frequency-deter mining circuit. This, of course, assumes that the injection frequency is itself stable, which can easily be achieved in practice.

Figs. .3, 4, 5 and 6 are scale reproductions of actual oscillograms illustrating features of operation and in particular illustrating, quantitatively, the presence of both the component frequencies per se and their intermodulation products. These oscillograms were made with the Fig. 1 circuit. In particular they illustrate how the desired functions are achieved without depreciation of the alternative functions of the organization as generators of sine wave component frequencies. That is, intermodulation is not attended by any extraneous distortion, so that there is a smooth, sine wave modulation of the 1,000-cycle frequency by the 20-cycle frequency as distinguished from a mere interruption at that frequency, or even of an unstable modulation short of actual interruption as might be expressed as an occasional overmodulation, either of which would not as well subserve all of the desired purposes.

Fig. 3 is an oscillogram of a voltage taken in the output circuit of Fig. 1. As in each of the other oscillograms and as has been assumed by way of example all along, the two component frequencies are 1,000 cycles and 20 cycles with a 60- cycle injection frequency. In this oscillogram the injection potential was 1 volt and this oscillogram was one of several illustrating the effect of varying the injection potential. This particular oscillogram of the series shows nearly the optimum injection potential, although a variation in either direction of as much as 40 per cent or thereabouts was found not to greatly change the purity of the modulated product. At greater divergences of injection potential the 20-cycle envelope becomes more ragged and then tends to break first into 30 cycles and then into 60 cillogram shows, in comparison with Fig 3, that there is a choice of places from which to derive the output side-band waves and also that it is possible to exercise a considerable discrimination in this choice since the wave at this point has nowhere nearly as great purity as if taken at the indicated output point in Fig. 1, as shown in Fig. 3. The conditions across this resistance R would tend to be nearly the same as across the input electrodes of the tube. The reason for good wave form. as shown in Fig. 3, as compared with Fig. 4, is that it is taken from the tuned circuit, which allows the side-band frequencies to flow and in turn suppresses any low frequency from flowing due to low impedance to the 20-cycle component and the like. That is; it removes the distortion shown in Fig. 4.

Fig. 5 is, similarly as Fig. 4, like Fig. 3. It differs in that the oscillogram was taken across the plate condenser Op. The wave is very evidently a 20-cycle wave, showing that although a 20-cycle wave is not self-sustaining as is the 1,000-cycle wave, it may be derived from the circuit in all of the purity that would attend, for example, the use of an LC self-sustained oscillator to generate such a wave, as in the instance of the 1,000-cyc1e wave. That is, the use of the injection frequency insures, with as gross a frequency-determining circuit as the RC circuit in question, as perfect a result as could be desired. Of course, this 20-cycle wave results from a demodulation of the side-bands illustrated in the two above oscillograms.

Fig. 6 is an oscillogram of a voltage taken across condenser C of Fig. 1. This voltage is the effective grid bias voltage of the oscillator tube. The oscillogram shows that the bias is varied at a 20-cycle rate and that this effect changes the gain of the tube to produce the 1,000-20-cycle output. This is not a pure 20-cycle wave due to distortion. For a fairly good 20-cycle wave form the best position would be across condenser Cp is in Fig. 5 because at that point there is high impedance to 20-cycle current and low impedance for the higher extraneous frequency currents present in the distorted 20cycle wave existing in the grid circuit. It was one of a series illustrating the effect of the use of different injection potentials, as in the instance of Fig. 3 and. which series as a whole showed the same sort of evolution. That is, with increase of injection voltage from zero there was first a SO-cycle wave with a 1,000-cyc1e ripple superposed on it, followed by an imperfect BO-cycle wave and then by the 20-cyc1e wave that is characteristic of the circuit. For this oscillogram, as for those of Figs. 3, 4 and 5, the injection voltage was 1.

As has been before stated, the Fig. 1 circuit has been used to demonstrate the efiicacy of the circycles, that is, into the injection frequency. The

Fig. 3 oscillogram is significant as showing a nearly perfect modulation in that the envelope accurately reproduces a 20-cycle sine wave. Also, although perhaps not quite so significant, there is complete modulation as indicated by the envelope coming all the way down to the axis.

Fig. 4 is an oscillogram like that of Fig. 3 but taken across resistance R. Otherwise the conditions are exactly as for Fig. 3, for example the same injection potential is used, and, therefore, are closest to optimum. A 60-cycie sine wave was superposed on the original of the oscillogram and is accordingly included in Fig. 4. This 0scuit of the invention, as shown by the above oscillogram. The following are the actual specifications of electrical values used in that circuit;

Tuning inductance=0.169 henry Tuning capacitance=0.15 microfarad C=0.02 microfarad R=1.8 megohms R1=100 ohms p=1 microfarad Battery voltage= Fig. 2 illustrates an alternative form of the invention as to the circuit for generating the 1,000-cycle wave and the connections of the tube elements to associated circuits. In these respects the figure merely indicates the verse.

7 tilityiof the invention since, having in mind :the ultimate result, there isverylittle choice .as between these two figures .or between the different specific expedients illustrated in them, and of which a great many others could have been illustrated. by additional figures. The particular purpose of Fig. 2, however, is to indicate the reason for the choice of the fill-cycle injection frequency and :to justify the seemingly increased,

complication required by the use :of such injection frequency. This teaching, of course, is as applicable to the Fig. 1 circuit as to "the Fig. 2 circuit. Except for this teaching the Fig. 2 cirouitdiffers from that .of Fig. -1 specifically in the use of what is sometimes called a reversed .feed backior tuned output feedbackoscillator which is only a slight variant from the Hartley oscillator of l, in its last analysis, andits'elf is known as one form of the Hartley oscillator, and in the useof ,a pentode tube as such as against the (ef* .tective) triode of Fig. l. The tube .is the same asin Fig. -1-.but here @the suppressor grid .9 and shield grid ill are separated from the anode and exercise :their .normal functions. The same tube arrangement andv connections of its electrodes .to associated circuits could have been used in the Fig. lcircuit. Theelementsof Fig..2.-not specifically mentioned above are the same as in Rig. 1 andare similarly identified in the drawing. The injection feature, which distinguishes the teaching of this figure, will be explained in greater .detail below.

In Fig. 2 the injection potential resistance B11135 been placed across the heater circuit of the tube with a switch H interposed in its circuit. It is evident that this injection resistance has precisely. the same relationship otherwise to the .circuit as .a whole, as in Fig. 1, just .as the RC circuit has the same relationship. .Howeuer, when switch ll is closed, the Gil-cycle current which is assumed to be used tor exciting the heater, .as it could have been assumed with respect to Fig. .1, takes on the new function of also supplying the. injection potential. This indicates that by the use of the expedient of the invention .calling for the use of v an injection frequency, there is .no implication whatever of the necessity for use of any additional circuit or plant, similarly asin the instance of elements BC. The switch ll makes possible the use of the circuit either to generate .the 1,000--cycle wave with its attendant possibilities of deriving the 1,000-cycle and .20-cycle waves per se, or the generation of the LOGO-cycle wave only uncomplicated by .the existence of otherfrequencies. This last function may be efficiently achieved even though the use of elements RC adapted for the 20-cycle modulation would tend -to somewhat affect the operation since a different choice of. values of these elements would be desirable for the most efiicient use .of the circuit as a Limo-cycle oscillator. In practice, however, this has been found to be of minor importance.

What is claimed is:

1. A self-modulated electric discharge tube oscillator comprising, an electric discharge tube having input and output electrodes and associated circuits all so interrelated as to cause the organization to generate a steady, substantially pure, wave of relatively high frequency, a relatively low frequency modulating wave source comprising. a resistance-capacitance combination specific to .said input electrodes for determining the modulating frequency, andan injecfrequency means connected to said associ- 8 ated circuits adapted :to coerce said low frequency combination and look its frequency into a-commensurable relation withits ownffrequency, said tube having a modulating as well as an amplifying characteristic whereby the organization as a whole is adapted .to generate steady, pure, waves of both said relatively high and relatively low frequencies together with intermodulation products of the same.

2. A self-modulated electric discharge tube oscillator comprising, an electric discharge tube having input and output electrodes and associated circuits all so interrelated as to cause the organization to generate a steady, substantially pure, carrier wave, a resistance-capacitancecombination specific to said input'electrodes and hayinga time constant corresponding approximately to the desired modulating frequency, an injection frequency source adapted to generate a wave having a commensurable relation to said modulating frequency, and coupling means between said injection frequency source and said resistance-capacitance combination whereby said injection wave may coerce said modulating .frequency circuit as in accordance with said commensurable relation, said tube having an amplifier-modulator characteristic whereby the organization as a whole is adapted .to generate steady, pure, waves of both the carrier and modulating frequencies as well as their intermedulation products.

3. An oscillator-modulator comprising an amplifier-modulator electric discharge tube having input and output electrodes, 2. feedback circuit interconnecting said electrodes and including an inductance-capacitance combination for deter mining the frequency of carrier oscillation thereby generated, a resistance-capacitance combination specific to-said input electrodes and having a time constant corresponding approximately to a desired modulating frequency, and an injection frequency source adapted to generate a wave having 'a commensurable frequency relation to said desired modulating wave, and means coupling the same to said resistance-capacitance combination, whereby the organization as a whole is adapted to generate a steady, pure, wave of the carrier frequency as Wll as to generate, by modulating and demodulating action, respectively, waves of combination frequencies and a steady pure wave of'the modulating frequency.

'4. The organization specified in claim 3 in which said resistance-capacitance combination also. constitutes an electrode-biasing-potential determining means for said carrier wave generating means.

5. 'An oscillator-modulator comprising an electric discharge amplifier-modulator tube having a cathode, control electrode, and anode, a feedback'circuit including a carrier-frequency-determining circuit between the anode-cathode and control electrode-cathode pairs of tube elements, a capacitance in circuit with said control electrode cooperating with a resistance also in said control'electrode circuit but at least partially in shunt to said capacitance, to bias said control electrode for efiective operation of said tube as an amplifier 'or modulator, the time constant of the resulting resistancecapacitance combination also corresponding approximately to a desired modulating frequency, an injection frequency source adapted to generate asteady wave whose frequency has a commensurable relation to said desired modulating frequency, and means coupling said source to said resistance-capacitance combination for coercing same at the commensurable frequency approximately corresponding to said time constant, whereby the organization as a Whole is adapted to generate, by oscillator action, a carrier frequency and, by modulator and demodulator action, respectively, a Wave having combination frequencies and a pure sine wave corresponding to the modulating frequency.

6. The organization specified in claim 5 including additionally means whereby said injection frequency source energizes the cathode of said tube.

7. The organization specified in claim 5 in which said carrier, modulating and injection frequencies are of the order, respectively, of 1000, 20 and 60 cycles and in which there is additionally a means for energizing the cathode of the 10 tube from the 60-cycle injection frequency SOHICG.

ALPHONS V. WURMSER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

